Indeed अभ्यास, practice, and वैराग्य (detachment), have been mentioned as the two means to असंप्रज्ञात-समाधि.
Of them since अभ्यास, which is dependent on some object, cannot be the cause of the objectless समाधि, therefore पर-वैराग्य (supreme detachment) itself which is not dependent on any object, is said to be the cause.
But अभ्यास becomes helpful as an indirect means to असंप्रज्ञात-समाधि through the medium of संप्रज्ञात-समाधि.
So it has been said in Sutra 3.7 (त्रयमन्तरङ्गं पूर्वेभ्यः॥७॥ as explained in detail before). To give in succinctly, as compared with the group of five disciplines viz. यम, नियम, आसन, प्राणायाम and प्रत्याहार , the three disciplines viz. धारणा (concentration), ध्यान (meditation) and समाधि (absorption), are more intimate practices for सबीज-समाधि.
The word समाधि, when it occurs among the group of disciplines, denotes अभ्यास itself; because समाधि in the primary sense of self-absorption is the goal and not a discipline.
तदपि वहिरङ्गं निर्वीजस्य॥८॥ (Yoga Sutra 3.8) “Even that group of three disciplines is an external practice in respect of निर्बीज-समाधि.
Even that group of three disciplines viz. धारणा, ध्यान and समाधि, however, is an external practice indirectly helpful with regard to निर्बीज-समाधि.
That is to say, for that निर्बीज-समाधि, however, पर-वैराग्य (supreme detachment) is absolutely the intimate practice.
This निर्बीज-समाधि, again, is of two kinds–भव-प्रत्यय and उपाय-प्रत्यय. (भवप्रत्ययो विदेहप्रकृतिलयानाम्॥१९॥ Yoga Sutra 1.19).
“The समाधि of the विदेह and प्रकृति-लय has for its cause (प्रत्यय) the mundane state (भव).
Of the aforementioned विदेह, who have achieved the सानन्द-समाधि, the निर्बीज-समाधि that comes as a result of some particular birth, particular medicine, particular incantation, or particular austerity is a भव-प्रत्यय–it is that which has the भव, mundane state, for its प्रत्यय, cause; it is that of which the प्रत्यय, cause, is भव, the mundane state characterized by the absence of discrimination between the Self and the non-Self.
भव-प्रत्यय means that which is caused by the mere fact of birth, as in the case of birds flying into the sky. (The विदेह and the gods are from their very birth endowed with such mystic powers as ‘becoming subtle’ etc.)
The idea is that this kind of समाधि should be spurned by people seeking Liberation, because it is a cause of mundane state again.